<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>Document</title>
    <style>
        button {
            width: 100px;
            height: 35px;
            text-align: center;
            font: 18px/35px "微软雅黑";
            margin: 0;
            padding: 0;
        }
    </style>
</head>
<body>
    <button id="btn">按钮</button>
    <script>

        
        // document.getElementById('btn').onclick = function(){
        //     document.getElementById('btn').style.background = 'red';
        //     document.getElementById('btn').style.width = '300px';
        //     document.getElementById('btn').style.height = '70px';
        //     /*
        //         边框
        //         文字大小
        //         文字颜色
        //         我统统想改
        //         ????? 多次获取元素
        //     */
        // }



        var btn = document.getElementById('btn');
        btn.onclick = function(){
           btn.style.background = 'red';
           btn.style.width = '300px';
           btn.style.height = '70px'; 
        }

        
    </script>
</body>
</html>